Sound reproduction



Oct. 22, 1935. w. H. oFFENHAUsER, JR 2,018,315

I SOUND REPRODUCTION Original Filed Dec. 18, 1929 2 Sheets-Shaml l y l.www y W W V J ATTORNEY Oct. 22, 1935. w. H. cFFENHAusER, JR 2,018,315

soUND REPRODUCTION Original Filed Dec.. 18, 1929 2 Sheets-Sheet 2 lINVENTOR W. H. OFFEN H AUSER ATTORNEY Patented Oct. 22, 1935 AuNrrizDSTATES `PA'rEm'{ori-ICE 2,918,315 lsoUNp nErnonUc'rroN Originalapplication December 18, 1929, Serial No. 414,878-, Divided and thisapplication April 2,

v1931, Serial No. 527,322

3 Claims.

In the reproduction of sound recorded upon a moving film, aconsiderableA number of difficulties are encountered. 'I'he particulardiiculty with which this case is concerned is that with respect to.change in volume, or more particularly, with respect to maintaining aproper ratio between the intended sound eiects and the sound produced byirregularities in the film, and emulsion and dirt, which causes what iscommonly referred to as ground noise. t

In order to maintain the. ratio of desired sound large with respect tothe ground noise,- it has been found impossible to produce thepianissimo effect with the same setting of the reproducing amplifiers aswell as reproducing from the same film, the forte eiect. It has,therefore, been necessary to provide some means for varying theamplification of the reproduced sound currents. In other wor thepianissimo must be recorded after greater amplification thanl the forte,and in reproduction the pianissimo must not be so much amplified.

Many means have been proposed for doing this, the simplest and mostcommon of which -is the simple manual variation of the amplification inreproduction. This has led to the improper sound reproduction of filmsdue to the, ignorance or y lack of feeling of the operator and, in somecases,`

to the entire loss of proper elect, amounting almost to ruining whatmight otherwise be a good sound picture.

Later development has been the preparation of a cue sheet which enablesthe operator to set hisA amplification at exactly the right point forthe various sounds of the lm. This, however, requires absolute attentionand does not permit small variations to take place frequently withinthespace of a scene. The result is, therefore, a littlek better than thatproduced by the undirected efforts of the control operator.

Mechanical and electro-mechanical means and methods have been proposedfor accomplishing the desired result. These methods might be roughlydivided into two classes: the first, in which an auxiliary record ofsome type is used to controll the volume in reproduction; and the secondclass, the one into whichthe present invention falls, a type of recordwhich will simultaneously .control the tone as well as the full range ofthe volume vof the sound. This latter method will be discussed'fullyhereinafter.

The type of control in which the auxiliary record isused falls roughlyinto two branches the rst, in which a simultaneously operated record isrun, such as a volume control phonograph record of the disc or filmphonograph type, or

even a perforated record similar to that used in a player piano; and thesecond class, in which the volume control record is incorporated on thesame lm with the sound record. The volume control record may take theform of either a photoelectric record from which the amplifier biasingpotential may be obtained, or from which a control `current to operatemeans for mechanically varying the amplifier bias is obtained. This 10control record incorporated in the talking moving lm may also take theform of a mechanical record such as perforations or indentations of thelm adapted to control a mechanical film control in an appropriatemanner.

15 The present invention has no distinctl bearing upon the foregoingbriefly .outlined methods of volume control. It, on the other hand,relates to the method of volume control in which a single sound recordhas incorporated therewith, features 'which enable the full control ofvolume as well as the control of tone. Another method falling into thissame general class has been suggested. In this method, the` mean audiocurrent in reproduction is varied so that the light falling upon thephoto cell is zero for low volumes as well as high volumes, with maximumsound impulses displacement. In this method, however, it is necessary inreproduction to have a special amplier having some sort of a time lagdevice in order to control the gain control of the amplifier.

In the present method, the tone frequencies are recorded either asdensity variations or area variations at full modulation, and the volumeis recorded as a variation in area or density respectively.

In reproduction the gain control of the reproducing device is set togive maximum amplification desired, and the control of volume would beautomatically caused entirely by the total variation in the lighttransmitted through the lm.

The process thus resides entirely in the recording in which the biasrequired to obtain a maximum modulation in recording the tone is adaptedto `control means for causing the appropriate area or density variationsto produce the gain control variation of the record.

As an example, when the very heaviest tones being recorded, say,by thevariable area method, the recorded tones would occupy the entire widthof the sound track. In this case, the supposedly clear portion of thepositive used in reproduction would be as clear` as possible, and as thetones 'in the sound being recorded change from forte yao to pianissimo,this clear portion of the record f lWasy maintained at full amplitude.

would be gradually shaded, completely covering up the ground noiseinherent in it at the same time that the variable area feature of therecord The amount of amplification which was necessary to ampliiy thetones picked up from the sound being recorded to actuate lthe soundrecording mirror at full amplitude would reciprocally reduce theintensity of the recording light so that in the positive, as theintensity of the reproducing sound changes from forte to pianissimo, theclear portion of the nlm which is indicative of the intensity of therecording light would change from the most brilliant to the leastbrilliant.

The operation, when a sound is recorded by variable density, is simplyreversed, the intensity of the light varying on each cycle of the audiotone from maximum to minimum and the width of' the record beingcontrolled reciprocally in the same manner as was the intensity of thelight in the nrst instance.

Having thus described my invention, attention is invited to theaccompanying drawings in which;

Fig. 1 represents a record made in accordance with the method of myinvention, in which the tone is controlled by variable density and thevvolume by variable area;

Fig. 2 is a record made in accordance with my invention in which thetone is controlled by variable area and the volume by variable density;

Fig. 3 is a schematic diagram illustrating the method of producing therecord of Fig. 1; and

Fig. 4 is a schematic diagram illustrating the method of producing therecord of Fig. 2.

Referring now more particularly to Fig. 1, there is shown a talkingmotion picture nlm I having a sound record portion II on the sidethereof. This sound record is of the variable density type, and it willbe observed that the record density changes from maximum densitytominimum density for each cycle of the audio frequency. In order tocontrol the actual volume, the effective area of the sound record isvaried from the full width at the portion I2, Where the tone is supposedto be forte, to minimum width at the portion I3, where theV tone to bereproduced is supposed to be pianissimo, thus producing a volume controlarea I4. If a light is passed through the sound record II and permittedto fall upon a photoelectric cell, and the current thus produced isamplined and reproduced through suitable loud speaking devices, it isobvious that the nuctuations of current produced by the light fallingupon the photoelectric cell in passing through the portion of the recordI2 will produce: the greatest possible variation in the loud speakercurrent, and, therefore, a sound of the greatest intensity; whereas whenthe light falling upon the cell is that passing through the record atthe portion I3, the variations of current are fed to the loud speakerdevices, and, therefore, the sound produced will be minimum. However, itis to be observed that the ratio of the sound current to the groundnoise current is at all times maintained constant, that is, the dirt andgrain irregularities aifecting the light passing through the nlm at theportion I3 of the record, affects the total amount of light only by thesame proportion that it does at the portion I2. In other words, withthis record being passed through a sound reproducing appa'- ratus,Whereas the groundl noise at the portion I2 will be considerable, thesound produced by the actual tone variations will be a great deal more,or, there will be a high ratio between the tone and ground noise. At theportion of the record I3, there will be a very much diminished groundnoise effect, and the total sound produced by the record will be alsodiminished, but they 5 will both be diminished in approximately the sameratio.

Referring now more particularly to Fig. 2, the sound strip II of the nlmI0 is shown as a variable area record, and the normally clear portions10 I5 of the nlm are shown as varying in density from the least densityat I2 to the maximum density at I3. The explanations with respect to thevariations of the tone reproduced from this record are the same as theexplanations with 15 respect to Fig. 1. It is seen that whereas thenuctuations of 'light falling upon the photoelectric cell through theportion I 2 of the record are maximum, and fluctuations caused by thelight 4passing through the portion I3 are mini- 20 mum, the ground noiseeffect at the portion I2 is maximum, whereas the ground noise effect atthe portion I3 is minimum. The shading of the clear portion of the nlmmay be arranged to keepthis ratio approximately constant and is 25 shownas near as possible to have the same occlusion of light as the'occlusioncaused by the narrowing of the nlm area of the nlm record of Fig. 1.`

As above stated, inthe reproduction from either 30 of these two types ofrecord, the light simply passed through thesound record in the ordinaryfashion and the reproduction is otherwise exactly the same as it is inthe usual sound reproduction froma talking moving nlm, the onlyexception be- 35 ing that the amplincation of the control apparatus isadjusted to give the maximum effect desired when a clear or full widthportion, or a maximum volume portion of the record, is passingthrough'the machine. tomaticallycontrols the volume of reproductionentirely by controlling the amount of light falling upon thephotoelectric device.

Brieny described, the methods of producing a nlm in accordance with thisinvention would be 4'5 similar to that producing the variable area, andvariable density record in common use at the present time. The variablearea type as shown infFig. 2`wou1d probably be most easily producedusing the present apparatus. lSuch an ap- 50 paratus modified to producethe record of Fig. 2 is schematically illustrated in Fig. 4 to whichattention is now invited. In this ngure, the current picked up by themicrophone 4I is suitably amplined at 43 and used to control the shutter55 or galvanometer 45 of the recorder in the usual 'mannen except thatamplincation regulator means 44 is provided to cause' the shutter orgalvanometer to operate it at a maximum amplitude at all times. Somesuch means are to 'oe 60 found in automatic volume control systems. Suchregulator means for adjusting the current being recorded are shown inFig. 2 of the patent to Sacia 1,623,756. The amount of gain controlcurrent necessary to cause maximum operation of the recording shutter orgalvanometer would be used to reciprocally vary the intensity of therecording light so that when the sound being recorded was maximum andvery little ampliiication was necessary tooperate the recording shutterat maximum, the recording light 46 would be at full brightness, Whereaswhen the sound being recorded is minimumand a great deal of amplincationis necessary to cause the shutter to work at fun capacity, the intensityof the iight The nlm then auo would be decreased. The reciprocalamplifier 4l is used to supply the current to the recording light 46.The nlm 40 is the negative of the nlm shown in Fig. 2 and, therefore,the representations of light and shading are the opposite of those shownin Fig. 2.

The recording of the lm shown in type I is practically as simple, asshown in Fig. 3. In this figure, the amplified recording current is usedto control the intensity of the light 36 ,of the usual variable densitytype of recorder, and the amplication of the light uctuations necessaryto cause full uctuation at all times is used to control the shutterwhich serves to screen a portion of the image to produce thevariationsin the width of record 38 produced on the moving ilm 30. Asshown a reciprocally controlled auxiliary amplifier 31 is used in orderthat the circuit of Fig. 3 may be the same as that of Fig. 4. In thiscase, the shutter is arranged to reduce the width of the sound track 38vto the least extent when the greatest amplification ofthe weakestsignals being produced by the microphone 3| is taking place in theamplifier .34. Under these conditions, of course, the greatest amount ofcontrol current is used to regulate the maximum intensity of light 36and therefore the least current flows to the shutter 35. It is obvious,howcver, that the reciprocally controlled amplifier 31 may be omittedand the shutter 35 arranged to give the least sound record width withthe least input current representing therefore the least amplificationof the input current by the amplification regulator 34. g

While I have briey outlined methods of producing the iilm of myinvention, it is to be understood that I am not to be limited by anysuch method of producing a film except as broadly set forth in theappended claims. I am therefore limiting my description of the method ofrecording to its essential elements, which are neces. sary to producethe record of my invention. I am 5 similarly limiting the description ofreproduction of my record it being understood that essential- 1y myinvention resides in the type 'of sound record and method, rather thanin any specic appa ratus.

Certain variations of either the recording or reproducing apparatus maybe made which fall clearly within the scope of my invention, which it ismy intention to denne in the appended claims. It is to be understoodtherefore, that I am not 15 to be limited to the specific embodimentshown and described for the purpose of illustration, butv by the scopeof my invention as set forth in the appended claims. By the term soundrecord in the following claims I refer to a record of 20 sound, asdistinguished from indicia of notes or a record of notes or individualnotes to be reproduced such as are used on music rolls for automaticpiano or organ actions.

I claim: 25

l. A talking motion picture record in which the sound is recorded as a.variable density record, and volu'me is recorded by variations in thearea of said record.

2. A talking motion picture record in which the 30 sound tone islrecorded as a constant amplitude variable density record and the volumeis'recorded as variations in the area of the record.

3. A film record comprising a sound-track in which` the tone consists ofa constant maximum 35 amplitude variable density record and the volumeconsists of a variable area record.

H. OFFENHAUSER, Jn.

